Re: understanding Debian support on ARM architecture
On Sun, 10 Aug 2014 20:10:56 +0100
Joe <joe@jretrading.com> wrote:
> On Sun, 10 Aug 2014 14:14:53 -0400
> Celejar <celejar@gmail.com> wrote:
>
> > On Sun, 10 Aug 2014 18:22:41 +0400
> > Reco <recoverym4n@gmail.com> wrote:
> >
> > > Hi.
> > >
> > > On Sun, 10 Aug 2014 17:09:58 +0300
> > > Martin T <m4rtntns@gmail.com> wrote:
> > >
> > > > Reco,
> > > >
> > > > thanks for this explanation! Could you please explain this
> > > > hardware enumeration provided by x86/x86-64 CPU's to kernel bit
> > > > more? What kind of information is provided to kernel in case of
> > > > x86/x86-64 CPU?
> > >
> > > Sure:
> > >
> > > 1) Obtain any x86 hardware.
> > >
> > > 2) Boot Linux.
> > >
> > > 3) Run lspci. Observe a non-empty result, which will probably
> > > include SATA, Ethernet, USB, Memory controllers and probably much
> > > more.
> > >
> > > 4) Repeat steps 1-3 with any ARM board (assuming successful boot, of
> > > course). Observe exactly one line that says (in my case, and that's
> > > good one, usually there's nothing at all):
> > >
> > > 00:00.0 Host bridge: Marvell Technology Group Ltd. 88F6281
> > > [Kirkwood] ARM SoC (rev 03)
> > >
> > > And that particular hardware has at least Memory, Ethernet, 4-port
> > > SATA controller and USB.
> > >
> > >
> > > That's they mean then they talk about hardware enumeration - it's
> > > all there yet ARM platform has no means to discover it or to tell
> > > Linux kernel its there.
> > >
> > > So, you count the hardware, produce device tree, compile it into the
> > > kernel - and you can work with said hardware.
> > >
> > > You have a different set of hardware - you'll need a different
> > > device tree. And that means a different kernel.
> >
> > Thanks for this explanation. I also run Debian on a Kirkwood platform
> > (a Seagate GoFlex Net (STAK100)) (in addition to my x86 hardware), and
> > I kept seeing all this talk about flattened device trees, and was
> > aware of the need for special kernels, but I never really understood
> > why ...
> >
> > http://forum.doozan.com/read.php?2,12096,12096
> >
> > Now, I'm still not sure about the difference between flattened and
> > non-flattened trees, and what they're relative advantages and
> > disadvantages are ...
> >
>
> One of the reasons for the complication is that all ARMs are not
> created equal. The ARM is not a processor, but a set of macros in a
> semiconductor design language. Various manufacturers are licensed to
> use the ARM core, and may add a variety of other hardware, effectively
> as subroutines. The chip may have a numeric co-processor or not. So
> there's no standardisation of hardware architecture such as the
> 'IBM-compatible PC' ('will it run Lotus 123?') had thirty years ago. The
> kernel needs to know what the composite chip contains and how to drive
> it, and how it talks to the rest of the system.
>
> For example, the Raspberry Pi, a well-known small ARM-based computer,
> uses a Broadcom 'System-on-Chip' processor, about which not much
> information is available. The kernel of Raspbian isn't actually part of
> Raspbian, but comes from the Raspberry Pi Foundation, and is closed
> source, and presumably is proprietary to Broadcom. I suspect that few
> ARM licensees provide full specifications of their devices.
Thanks. I understand the basic situation WRT ARM devices; I just don't
know the specifics about device trees, flattened and non-flattened.
Celejar
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